The creation of finished, bound books using “print on-demand” processes and electronic print engines is becoming ever more popular for publishers of all sizes. Unlike traditional printing processes, which employ fixed plate presses to transfer images to the web or sheet, electronic printing allows for the creation of smaller print runs that can be customized, on a book by book basis. To maximize efficiency, pages for finished books are often printed on a larger overall web or sheet, which is subsequently cut and slit into the desired page dimensions. These cut pages are thereafter fed to a collection point and stacked into finished “book blocks.” The book blocks are trimmed into squared-off stacks using a three-knife trimmer, and directed to a binding process, wherein an outer cover is bound to the book page stack.
The creation of book blocks often involves a number of manual steps. For example, printers often generate a plurality of page images on a larger sheet (sized 11×17 inch, for example). These images must be separated into separate pages of appropriate size. The manipulating of sheets from the printer can entail forming secondary stacks and thereafter physically moving and directing the stacks through cutters and slitters to generate the final set of pages in the appropriate page order. This book block stack is then directed to the trimming and binding process by another set of manual tasks. Any defective pages or stacks are removed and dealt with by hand, typically requiring the reassembly of the defective stack with new replacement pages as appropriate.
Currently available electronic printers, such as the Indigo™ 5500 Digital Press, available from the Hewlett-Packard Company of Palo Alto, Calif., offer a wide range of print versatility at high levels of print quality. Such printers allow for the duplex (two-sided) printing of full color photo-quality images on a variety of paper types (matte, glossy, etc.), fed from sheets. These printers, and other of similar type, offer a high throughput speed (for example, currently up to approximately 70 pages per minute (ppm) for color print and up to approximately 270 ppm for monochrome print). Completed sheets, typically containing multiple, two-sided page images in appropriate sizes are stacked on an output stack that is subsequently divided into appropriate pages for binding in a finished book. A printing computer and associated software application(s), which interconnected with the print engine controller, organizes the order and location of images on each side of each sheet.
To fully take advantage of the speed and versatility of such electronic printers, the automation of the handling of output sheets is highly desirable. In general, it is desirable that the output sheets be automatically cut and slit to appropriate sizes and that this sizing process allow for the creation of accurate, full-bleed (e.g. marginless) pages that are ready to stack into completed books. It is further desirable that the automated cutting and slitting process occur at a speed that can accommodate the output speed of the printer, enables the identification and handling of defective pages and stacks and can be variably set to handle a wide range of page sizes, shapes and numbers on a given output sheet.